Exploring new links between crystal plasticity models and high-energy X-ray diffraction microscopy

Highlights

• Crystal plasticity model development requires targeted experimental validation.

• HEDM experiments provide new insights into microstructure dependent plasticity.

• Direct HEDM-simulation comparison offers a pathway for future development.

Abstract

The advancement and transition of computational materials models requires corresponding developments in experimental methods to provide new phenomenological insights as well as quantification of model performance. In this article, we explore the natural links between crystal plasticity modeling and a suite of high-energy X-ray diffraction experimental techniques referred to as high-energy diffraction microscopy (HEDM). HEDM methods provide information such as the elastic strain state of individual grains and the distribution of crystallographic orientations. As a non-destructive characterization method, pairing HEDM with in situ mechanical testing enables tracking of material state evolution through quantitative measurements that may be directly compared to a simulation. We highlight some recent successes in this area and provide suggestions for future research.

Introduction

The link between experimental characterization and performance modeling in materials science and engineering is an enduring tenet that remains as strong today as ever before, including for the field of crystal plasticity. At its origin, crystal plasticity emerged due to a lack of theory to explain observed experimental phenomena. The theory of the dislocation as a facilitator of plasticity in 1934 resulted from painstaking mechanical testing and characterization of single crystals [1], [2], [3], [4], [5]. Since that time, crystal plasticity models have evolved in conjunction with advances in mechanical testing and materials characterization capabilities, as well as access to constantly improving computational resources. Today, a variety of sophisticated computational tools have been developed to predict the anisotropic elastic and plastic deformation of crystalline materials subjected to a multitude of mechanical and thermal stimuli (for a detailed review of the field, please see [6], [7], [8], [9] and the references therein).

Despite decades of maturation, a lack of experimental validation studies that capture the salient details of deformation at the corresponding length scales has impeded implementation of crystal plasticity models into modern engineering workflows [10], [11]. In particular, mesoscale experiments capable of characterizing and tracking the behavior of individual grains within 3D polycrystalline ensembles are critically needed in order to provide insight into the influence of local boundary conditions on the micro-mechanical response [12], [13]. Additionally, there are many details to consider that drive the behavior of a specific material: anisotropic elasticity, operating plastic deformation mechanisms (e.g. dislocation glide on particular slip system(s), deformation twinning), presence of secondary phases and/or voids, etc. Further complicating modeling efforts is the fact that the material also evolves during plastic deformation, leading to, for example, lattice reorientation and slip system hardening. In short, accurate prediction of crystal-scale deformation represents an enormously challenging problem area that requires targeted experimental capabilities which evolve hand in hand with a model.

Recently, synchrotron X-ray techniques known alternatively as three-dimensional X-ray diffraction (3DXRD) or high-energy diffraction microscopy (HEDM; we will use this terminology throughout for consistency) have matured to the level that they are establishing a standard from which to guide modeling efforts. These tools provide the exact mesoscale, multi-modal in situ characterization data that is needed for direct comparison with crystal plasticity simulations, thus providing an opportunity to test the predictive capabilities of a model and either gain confidence in its performance or identify aspects where further improvements are needed. This link between HEDM and crystal plasticity modeling, in particular for metallic materials, will be the subject of the remainder of this manuscript.